With recent downsizing and improvement in quality of electronic devices, electronic components used in the electronic devices, such as a push switch, are required to be small and to provide less strain and good feel to fingers during operation. A push switch is required to be able to be pushed after being turned on, that is, to have a stroke after turning on (hereinafter referred to as “an over-stroke”) in addition to an operation stroke until the switch is turned on (herein after referred to as “an on-stroke”), providing a long operation stroke and a good operation feel.
FIG. 7 is a front cross-sectional view of a conventional push switch disclosed in Japanese Patent Laid-Open Publication No. 10-92260. FIG. 8 is an exploded perspective view of the switch. Columnar caulking projection 1A is provided at each corner of the top surface of box-shaped case 1 made of insulating resin. Central fixed contact 2 coupled to connection terminal 2A and two outer fixed contacts 3 coupled to connection terminal 3A are fixed on the inner bottom face of case 1 by insert molding. Movable contact 4 made of resilient thin metal plate is mounted on outer fixed contacts 3.
Movable contact 4 has outer periphery 4A having a annular ring shape, and tongue 4B extending from outer periphery 4A to the center of the ring shape. Tongue 4B is coupled to outer periphery 4A at junction portion 4C. Tongue 4B is bent at junction portion 4C to incline upward. Outer periphery 4B of movable contact 4 is mounted on outer fixed contacts 3 to electrically contact fixed contacts 3. Tongue 4B faces central fixed contact 2 by a predetermined clearance between tongue 4B and fixed contact 2, providing a switch contact.
Elastic body 5 made of elastic material, such as elastomer, has rod portion 5A at the upper part of body 5, and conical portion 5B at the lower part of body 5. Conical portion 5B which is hollow and thin has an opening which opens downward. Elastic body 5 further has projection 5C projecting downward from the center of conical portion 5B opening downward. Projection 5C faces tongue 4B of movable contact 4 by a predetermined clearance between projection 5C and tongue 4B. Lower end 5D of conical portion 5B is mounted on outer periphery 4A of movable contact 4.
Cylindrical operating body 6 made of insulating resin is mounted on rod like portion 5A of elastic body 5 and has an opening at the lower part of body 6. Operating body 6 includes operating portion 6D, i.e. the upper part of the operating body, sidewall portion 6A extending downward from operating portion 6D, engaging portions 6B protruding outward from sidewall portion 6A, and stopper claws 6C projecting from the lower end of sidewall portion 6A. Each of engaging portions 6B has a predetermined width and extends vertically. Each of stopper pawls 6C projects from a position different from engaging portion 6B at the end of sidewall portion 6A.
Cylindrical cover 7 made of insulating resin has through-hole 7A formed therein. Operating portion 6D, i.e. the upper part of operating body 6, projects upward thorough through-hole 7A. Cover 7 has notches 7B in the lower part of cover 7. Each of notches 7B is engaged with a corresponding projection 1A and attached to case 1.
Grooves 7C extending vertically are formed in the inner wall of cover 7. Engaging portions 6B of operating body 6 are inserted into grooves 7C. Engaging portions 6B are engaged with grooves 7C to allow operating body 6 to be guided to be movable upward and downward smoothly without rattling. In an ordinary status shown in FIG. 7, stopper claws 6C of operating body 6 are engaged with the inner surface of the top face portion of cover 7 around through-hole 7, preventing operating body 6 from dropping thorough through-hole 7A.
Recesses 7D opening inside are formed in portions of the sidewall of cover 7 below stopper claws 6C and extend in vertical directions in which stopper claws 6C are positioned. Each recess 7D receives a stopper claw 6C positioned therein to allow claw 6C to be movable in recess 7D when operating body 6 moves downward. The sidewalls of recesses 7D guide stopper claws 6C. Grooves 7C and recesses 7D restrict engaging portions 6B and stopper claws 6C to be movable only upward and downward, respectively, thereby preventing operating body 6 from rotating or dropping out upward.
An operation of the conventional push switch will be described below.
When operating portion 6D in a turned-off status shown in FIG. 9 is pushed with operating force F1, operating body 6 presses elastic body 5 downward direction D1, thereby causing conical portion 5B of elastic body 6 to deform. Upon deforming, conical portion 5B provides a light click feel, and simultaneously to this, projection 5C of elastic body 5 in a presses tongue 4B downward. This action causes the bottom face of tongue 4B to contact central fixed contact 2, thus establishing electrical connection between central fixed contact 2 and outer fixed contacts 3, that is, between connection terminals 2A and 3A.
When the pressing force applied to operating portion 6D is removed, elastic body 5 and movable contact 4 return to their original shapes shown in FIG. 7 by their own restoring force. Thus, the electrical connection between connection terminals 2A and 3A is broken.
FIG. 10 shows a relation between the operation stroke and operating force F1 in downward direction D1, in which the vertical axis represents the operation stroke, and the horizontal axis represents operating force F1. The switch is turned on when the operation stroke reaches point P. In other words, range A1 where the operation stroke ranges from 0 to point P is the on-stroke. The switch is turned on in a portion where the operation stroke exceeds point P.
The conventional push switch has no portion which deforms further after conical portion 5B of elastic body 5 deforms to cause the switch to be turned on. In other words, as shown in FIG. 10, the switch provides almost no operation stroke in range A2 where the operation stroke exceeds point P, not providing a long over-stroke.